The present invention relates to improvements in bit holders used with apparatus for grinding the hard metal inserts or working tips of drill bits (percussive or rotary), tunnel boring machine cutters (TSM) and raised bore machine cutters (REM) and more specifically, a safe, simple, compact, yet effective locking means for a wide range and number of bit sizes and types within a bit holder fixture holding one or more bits.
In drilling operations the cutting teeth (buttons) on the drill bits or cutters become flattened (worn) after continued use. Regular maintenance of the drill bit or cutter by regrinding (sharpening) the buttons to restore them to substantially their original profile enhances the bit/cutter life, speeds up drilling and reduces drilling costs. Regrinding should be undertaken when the wear of the buttons is optimally one third to a maximum of one-half the button diameter.
Manufacturers have developed a range of different grinding apparatus including hand held grinders, single arm and double arm self centering machines for setting up two or more bits to be ground, mobile machines for grinding on the road or in a workshop and grinders designed specifically for mounting on drill rigs, service vehicles or set up in the shop.
Conventional locking means for a wide range and number of bit sizes and types within a bit holder used with existing machines are either too slow and prone to wear or too complicated for simple installations. The conventional manual locking means used with current bit holders utilizes a rotating screw type locking means with a lever or knob to lock the drill bits in place are cumbersome and do not allow for fast movement between maximum and minimum settings as the screw or threaded rod has to be rotated until the desired location is reached. The other conventional locking means consists of a cylinder that has a piston rod that retracts and extends by operating a manual valve. This type of locking means requires supply lines between a compressed air or hydraulic source to operate. Cylinders in conventional locking means are sized so that they consist of a piston rod that has a long enough stroke to achieve desired range of movement between maximum and minimum settings. This can both complicate installation as well as limit the configuration of the locking means configuration. For example, it would be rather difficult and space intensive to install multiple locking means using multiple cylinders in a rotating application.
The present invention provides a manual locking means for a bit holder fixture with two adjustments. A macro adjustment allows for quick positioning of a pressure plate against the body of the bit(s). A micro adjustment locks the bit(s) in place by applying pressure against the skirt or shank of the drill bit(s). By keeping the locking means safe, simple, effective and compact, it allows multiple locking means to be installed with ease within a bit holder fixture, as deemed necessary. Improved operator safety is achieved by separating macro and micro adjustment so that micro adjustment is used to apply the necessary pressure to lock bit(s) in place.
Further features of the invention will be described or will become apparent in the course of the following detailed description.